TBY-753A type fast charging regulated power supply circuit diagram

 　　The TBY-753A fast charging regulated power supply is a must-have portable device for backpack radios. It adopts pulse width modulation and its core component is the SGl524J chip produced in the early days of the American Silicon Communication Company.

The machine provides 12V, 24V stable voltage, and can also quickly charge　　12V, 24V/4Ah, 7Ah nickel-cadmium battery packs , and has protection functions such as AC over-under voltage, output over-voltage, over-current and over-charge, etc. It is a good product charging regulated power supply.

　　1. Working principle

　　SGl524J pulse width modulator, TEAll00 voltage negative increment detector, LM293 double-limited voltage comparator.

　　The AC220V mains power is filtered by the LPl power supply noise filter and rectified by U1, and a 300V DC voltage is established on the C5 and C6 capacitors, which is provided to the high-frequency power converter composed of V4, V5, T3, etc.; the other path is rectified by the T1 transformer U2 Then it provides the sampling voltage to U7, and provides 12V working voltage to the whole machine after being stabilized by U3.

　　The power supply of SGl524J pulse width modulator is supplied by 12V voltage through the power control switch tube Vl (3DGl2D). R6 and C9 determine the working cycle of the oscillator in the integrated block. The RC feedback network composed of C7, C8, R5 and R7 makes the amplifier in the chip work more stably. A push pulse with a width of 0.5μs~5μs is output from pins 12 and 13 to drive V2 and V3 (S8050) to work alternately, and then output from the secondary winding of pulse transformer T2. to drive two power transistors (C2307). D9, D10, C12, R18, and C32 form a spike absorption circuit. The secondary winding output of the high-frequency transformer is filtered by 1V1 and 1V2 high-frequency rectifiers Ll, ​​C15, and C16 to obtain the required DC voltage.

　　The DC voltage output by 1V3 is connected to line A at the 12V voltage stabilizing terminal through switches S4-2 and S2-2 to provide sampling voltage for D4, RP5, R23, and wire B is connected at the 24V voltage stabilizing terminal to ZD3, D3, RP4. , R24 provides sampling voltage; connect C line at the 24V charging terminal to provide sampling voltage for ZD2, D2, RP3, R25 (adjust the numbers of RP3, RP4, RP5

　　value can change the output voltage). The changing voltage extracted by the sampling circuit is input to the inverting input terminal of the error amplifier through pin ①. The reference voltage provided by pin 16 is input to the positive input terminal of the error amplifier through pin ②. After comparison and amplification, the error voltage is output, thereby controlling The width of the output pulse. To achieve the purpose of voltage stabilization.

　　2. Protection circuit

　　The machine has a variety of protection functions, including AC over-voltage and under-voltage protection, output over-voltage and over-current protection, battery overcharge protection, anti-impact current protection, etc.

　　1. AC over-voltage and under-voltage protection.

　　U7, RPl, RP2, etc. form AC over-voltage and under-voltage protection. The unstable DC voltage rectified by U2 is divided by R30 and R31 and then input to the ③ and ⑥ pins of the voltage comparator LM293. The 12V voltage stabilized by U3 is divided by RPl and RP2 and then input to the LM293 pins respectively. Pin ② and pin ⑤, when the voltage of pin ③ is higher than the set value of RP1, pin ① outputs a high potential, and drives D16 through R35 to illuminate, indicating AC overvoltage; through R36, Dll, and D5, the thyristor Q3 is triggered to conduct , Make V1 cut off, SGl524J has no power output, to achieve the purpose of protection; the other path triggers the thyristor Q4 to conduct through D14, so that V6 conducts, and DL emits an alarm sound. When the voltage of pin ⑥ is lower than the set value of RP2, pin ⑦ outputs high level, and drives D15 through R34 to emit light, indicating AC undervoltage; triggers thyristor Q4 through R37 and D17 to realize undervoltage alarm, but the undervoltage is not cut off. output, still works.

　　2. Output over-voltage and over-current protection.

　　ZD1, R26, Q2, etc. form the output overvoltage protection. When the sampling circuit fails, the 12V/24V switch is damaged, or the power supply is out of control due to live conversion, and the output voltage exceeds the ZDl voltage regulation value (38V), ZDl breaks down, and the thyristor Q2 is triggered, causing V1 to cut off, and SGl524J stops working. No voltage output. R check, RP6, integrated block ④, ⑤ pins, etc. form an overcurrent protection. When the load current flows through the R check, a negative voltage is generated at the ⑤ pin of the integrated block (relatively speaking). The greater the current, the more negative the ⑤ pin voltage is. , the greater the voltage difference between pin ④ and pin ⑤. When the voltage of pin ④ is 200mV higher than the voltage of pin ⑤, the current limiting circuit inside the integrated block acts, the pulse modulator stops working, and there is no voltage output. (The voltage difference between pin ④ and pin ⑤ consists of two parts. One is the positive voltage from pin ④ to ground, and the other is the negative voltage from pin ⑤ to ground. When the R check remains unchanged, adjust RP6 to change the voltage from pin ④ to ground. By increasing the positive voltage, you can change the voltage difference between pins ④ and ⑤, thereby adjusting the overcurrent protection preset value.

　　3. Anti-battery overcharge protection.

　　U5 (TEAl 100), ZD4, ZD5, etc. form the anti-battery overcharge protection. The charging output is sampled and tested by ZD4, ZD5, R44, R45, R46, and R47, and is input to pin ⑦ of the integrated block through the S4-1 switch. Pin ⑧ is the battery capacity selection switch. When the negative increment value of the battery voltage reaches the preset value, pin 15 outputs a jumping DC voltage, and R4l drives D12 to light up and flash, indicating that charging is completed. R29, D6, and D5 trigger the thyristor Q3 to conduct, causing Vl to cut off. SGl524J stops working without power supply and charging stops.

　　4. Anti-impulse current protection.

　　The anti-impulse current protection is composed of R28, Ql, J1, and R2. When the AC power is turned on, because JKl is not closed, R2 is connected in series to the power conversion circuit as a current-limiting resistor to limit the starting current. When the machine works normally , the output voltage triggers the thyristor Q1 through R28 , J1 is powered and JKl is closed, and R2 is short-circuited to reduce power consumption.