TL494 high voltage input step-down DC-DC converter

Common DC-DC applications are mostly suitable for lower Vin/Vout voltages (less than 30V-40V). It is rare to have a higher voltage input. This article introduces a buck converter that uses TL494 as the controller and can work at 60V input.

The circuit can be used for higher voltage by modifying the part specifications appropriately. This circuit operates at 110Khz with an efficiency of more than 80%. The output current can be between 0-2.2A (set by R5)

The driving voltage of the switch MOSFET (IRFW630A) is taken from the bootstrap circuit, so that the gate signal can always be about 10V higher than the input voltage. The advantage of using MOSFET is that it can work at high frequency and reduce the loss when it is turned on. The high operating frequency of the circuit also reduces the size of the inductor.

Component selection:

D7 should use an ultra-high frequency fast recovery diode. Here we use HER303. HER304-307 can also be used but the conduction voltage drop is slightly higher. For Schottky diodes, choose a model with a withstand voltage greater than the maximum input voltage;

C11 and C12 should be capacitors that can work at high frequencies and have small ESR. Low-frequency capacitors may even heat up significantly and be damaged quickly, and the ripple is also very large.

All small transistors use the common 2N5551, with a withstand voltage of 150V and a decent switching speed;

When selecting MOSFET, the withstand voltage should be higher than the possible maximum input voltage, and the smaller the on-resistance, the better. For example, if VINmax:50V, 60N06 is sufficient.

Power inductor: Use the common yellow-white iron powder core (outer diameter * inner diameter * thickness: 13 * 7.5 * 6.5). Wind 50 turns of 0.4mm enameled wire in parallel, and the inductance is about 120UH. Note that black cores cannot be used here (large inductance is easy to saturate).

This inductance is only suitable for the drawing conditions. If there are major changes, please change it yourself.

The protection diode is not small. If the switch tube breaks down, VOUT=VIN, which will directly damage the load! Use a 1W voltage regulator tube, and the nominal voltage is several V higher than the output voltage. A safer approach is to use a unidirectional thyristor plus a voltage regulator tube and a resistor protection circuit.

other:

Output voltage setting: R9

Output current limit: R5

Maximum duty cycle setting: R3 (without R3, the duty cycle can reach the maximum, which is suitable for the case where the input-output voltage difference is small)