Thursday, October 2, 2014
Simple IC 555 DC to DC Converter Circuit
When using a digital measuring instrument with another electronic circuit it is often necessary or desirable to completely separate the supply for the meter from that for the rest of the electronics.
The ` problem can be solved by using two separate supplies, but it can also be done using a single supply and a DC—DC converter. The type of converter described here is quite compact and can deliver a current of about 50 mA. p The circuit consists of an astable multivibrator (IC1), which switches the voltage supply for a transformer (Tr!) on and off via a transistor (T1). The transformer secondary voltage is ha|f—wave rectified and smoothed. The output voltage is then limited by zener diode D5. I The transformer used should have a ratio between the windings of 1:1. The firing transformer used for thyristors is ideal for the iob, but a small audio transformer (frorn a pocket radio) is also suitable. The frequency and pulse width of the circuit can be adapted to the type of transformer used by means of P1 and P2. Firing transformers give the best results at frequencies of about 100 kHz, while audio trans- formers usually work best between 0.5 and 40 kHz. The transformer must, of course, be connected witl· correct polarity. The frequency is found as follows:
F 0.7x (P1 +P2+ R1 + R2) xC1
tchargg = X X
tdigchargg : 0.7 X X C1.
The ` problem can be solved by using two separate supplies, but it can also be done using a single supply and a DC—DC converter. The type of converter described here is quite compact and can deliver a current of about 50 mA. p The circuit consists of an astable multivibrator (IC1), which switches the voltage supply for a transformer (Tr!) on and off via a transistor (T1). The transformer secondary voltage is ha|f—wave rectified and smoothed. The output voltage is then limited by zener diode D5. I The transformer used should have a ratio between the windings of 1:1. The firing transformer used for thyristors is ideal for the iob, but a small audio transformer (frorn a pocket radio) is also suitable. The frequency and pulse width of the circuit can be adapted to the type of transformer used by means of P1 and P2. Firing transformers give the best results at frequencies of about 100 kHz, while audio trans- formers usually work best between 0.5 and 40 kHz. The transformer must, of course, be connected witl· correct polarity. The frequency is found as follows:
F 0.7x (P1 +P2+ R1 + R2) xC1
tchargg = X X
tdigchargg : 0.7 X X C1.
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