We can use a CMOS nand gate or inverter gate and two transistors into the current controlled oscillator circuit (CCO). In Figure 1 use two inverters are connected together as a astable multivibrator circuit.
Figure 1 the normal astable multivibrator CCO circuit.
If the output of N1 is “0”, and C1 will start be charged through T1, until there is voltage exceeds the threshold of N1, cause output N1 is “0” and output of N2 is “1”. Then,the transistors – T1 will work reversed as before, is emitter and collector lead will work alternately, and C1 will also charge with reversed polarity.
When voltage at the collector lead of T1 lower than the threshold voltage level of N1, output of N1 will be “1” then the original process was repeated again.
T1 and T2 in this circuit are connected together as the current mirror circuit, by collector current of T1 (the same current that charge to C1) will be reflect current to T2 and this current is controlled by the base current.
If both transistors have same feature, the same collector current. These devices frequency of approximately 4-100 Khz.
When transistor T1 conducts in reverse, T2 will stop, and cause the bias voltage back to junction of base and emitter. If the supply voltage more higher than +5V, this junction maybe damaged. But low current and voltage under +5V so no dangerous.
Figure 2 the improved CCO circuit using CMOS
In Figure 2 is improved circuit to reduce the risk of damage while working at T1, by bridge diodes D1 to D4 as setting direction of current flow to T1 and T2 correctly all times.
How to application
We maybe apply with photo diodes and photo transistors to use the light control the circuit.
Parts you will need.
IC1___CD4011 or CD4049
T1,T2__TUP___BC557 PNP transistor
D1-D4__DUS___1N4148___75V 150mA Diodes
R1_____1K Resistor 0.25W
C1_____0.1uF 50V____Ceramic capacitor
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