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jimmc101 · 7th Apr 2020, 3:13 pm

The 1N4148 is a small signal silicon diode and is the correct part for D6, 7 & 8. The zener diode reference must be a mistake.

Section C of the HEF4093 forms a relaxation oscillator, without D6 and R11 the mark:space ratio would be approximately 1:1, D6 and R11 modify this to approximately 5:1 so that the LED is only on for 20% of the time.

D7, R4 and R13 are a puzzle they appear to be a crude attempt to offset the threshold of section D of the '4093, why I don't know.

D8 allows C3, R5 & VR1 to set the ON time once triggered, it stops C3 discharging back into the 4093.

To repeat use your 1N4148s the are correct for this circuit.

Jim

7th Apr 2020, 3:13 pm	#2
jimmc101 Heptode Join Date: Mar 2009 Location: Portsmouth, Hampshire, UK. Posts: 674	Re: Zener diode problem with Banggood kit. The 1N4148 is a small signal silicon diode and is the correct part for D6, 7 & 8. The zener diode reference must be a mistake. Section C of the HEF4093 forms a relaxation oscillator, without D6 and R11 the mark:space ratio would be approximately 1:1, D6 and R11 modify this to approximately 5:1 so that the LED is only on for 20% of the time. D7, R4 and R13 are a puzzle they appear to be a crude attempt to offset the threshold of section D of the '4093, why I don't know. D8 allows C3, R5 & VR1 to set the ON time once triggered, it stops C3 discharging back into the 4093. To repeat use your 1N4148s the are correct for this circuit. Jim