Common DC-DC applications are mostly suitable for lower Vin / Vout voltage (less than 30V-40V). For the case of higher voltage input is rare, this article introduces a buck converter that can work at 60V input with TL494 as the controller.
Appropriate modification of part specifications can be used for higher voltage. This circuit works at 110Khz and the efficiency is higher than 80%. The output current can be taken from the bootstrap circuit at the drive voltage of 0-2.2A switch MOSFET (IRFW630A), so that the gate signal can always be higher than the input voltage by about 10V. The advantage of using MOSFET is that it can work at high frequency and can also be reduced Loss at turn-on. The high operating frequency of the circuit also reduces the size of the inductor.
Component selection:
D7 should use ultra-high frequency fast recovery diode. Here, HER303 is used, but HER304-307 can also be used, but the turn-on voltage drop is slightly higher. For Schottky diodes, choose a model with a withstand voltage greater than the highest input voltage;
C11 and C12 are selected to be able to work at high frequency and ESR is small, low-frequency capacitors will even significantly heat up and quickly damage, the ripple is also very large;
All small transistors use the common 2N5551, withstand voltage 150V, and the switching speed is acceptable;
The selection of MOSFET, the withstand voltage is higher than the maximum possible input voltage, the smaller the on-resistance, the better, for example, VINmax: 50V, 60N06;
Power inductor: use the common yellow-white iron powder magnetic core, (outer diameter * inner diameter * thickness: 13 * 7.5 * 6.5). The 0.4mm enameled wire is wound three times with 50 turns, and the inductance is about 120UH. Note that the black core cannot be used here (the inductance is large and it is easy to be saturated).
This inductance is only suitable for drawing conditions, if there are major changes, please change it yourself.
There is no shortage of protection diodes. In the event of a breakdown of the switching tube, VOUT = VIN will directly damage the load! With a 1W regulator tube, the nominal voltage is a few V higher than the output voltage. A safer approach is to use a unidirectional thyristor plus a voltage regulator tube and a resistance protection circuit.
Output voltage setting: R9
Output current limit: R5
Maximum duty ratio setting: R3 (without R3, the duty ratio can reach the maximum, suitable for the case of small input and output pressure difference)
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